Manufacture of propellants



March 1, 1960 w. M. HUTCHINSON 2,926,336

MANUFACTURE OF PROPELLANTS Filed March 7, 1955 3 Sheets-Sheet l TIME- DELAY RELAY MANUAL RESET HYDRAULIC FLUID MANUAL RESET INVENTOR. W. M. HUTCHINSON BY M 4% ATTORNEYS March 1960 w. M. HUTCI-IIINSON 2,926,386

MANUFACTURE OF PROPELLANTS Filed March 7, 1955 3 Sheets-Sheet 2 FIG. 2.

INVENTOR. W. M. HUTCHINSON Bi /WWW ATTORNEYS March 1, 1960 w. M. HUTCHINSON 2,926,386

MANUFACTURE OF PROPELLANTS 3 Sheets-Sheet 3 Filed March 7. 1955 INVENTOR W.M HUTCHINSON AT TOR N EYS i' invention relates t the manufacture of propellants; Ip- -on e ofits aspects itrelates to a method and apparatus United. Str w Pare f Q7 v 2,926,386 6 est tes Mar. 1. a

However,- whefiopera'tin'g in this" mariner, accurate metering of the'plastic material isdifiicult, resulting in non-uniformity of grains and also deaeratio'ni'of the propellant material during the molding operation is difficult if not impossible. Furthermore there is no means for kneading the propellant during the compression molding operation.

Injectionmoldingprocedures appear to eliminatethe foregoing 'problen'is" in that" such methods can be operatedunderhigh pressures, provide satisfactory working of the material during the constriction and increased rate of flow ofmaterial'occasioned by the injection nozzle and furthermore these'methodscan also provide the necessary dwell period. However, when operating by this method, adequate'deaeration is quite difiicu'lnif not impossible and furthermorethe low' cap'acity of conventional injection for themanutacture oi grainsiof propellants havinghigh plastic" yield points. 1 In another oi its-aspects, it relate-s to a; combination ofex'trusion and injection methQd'sQof mqlding propellan-ts so as-to'exclude free space from within the propellant grain and from between the propellant grain and tlie mold. I g p 7 V H w. Recently "it; has been discovered that superior solid propellant mixturesare obtained comprising a solid oxi- I -dantsuch as ammonium--nitrateor ammonium perchlorate and .a rub EerYbinderirnaterial such as-a copolymer of butadiene arid a vinylpyr'idine or other substituted heterocyclie nitrogen basecompound, which after incorporation is curedb'yl a quaternization reaction or a vulcanization reaction. 1 Solid propellantrnixtures ofthisnatur'e' and a process for their production are: disclosed "and claimed a in oopendingiapplicationserialiNo 284,447: filed April 25, .1952, byW. B. Reynolds and J. Pritchardl a Solid propellant mixtures manufactured according to the above described process aresemi-solid plastic compounds, phone curing, which present problems in thernolding of fease-boride propellants. In thepreparation of caseliqnded pr opellaiits itfis necessarydhat the casing be com- .pletely filled, that the propellant be-properly deaerated,

prior to' bir'igrrioldd 'infirial-jform', and that the molded forrn shall, not-become distort rfioldifig pressure is]relea'sed.- These pro-'p'ellant" com- J- from relaxation! When phsitions containin'gka solid'joxidaht "mafia" binder, having plastic properties 'inlthe' uncnre'd state cannot be dissolved in a sel e'm' or otherwise reduce a a fluid stateYand 'eur'eafiina; a monta e: u therein" in same manner, therefore, pressure rnethodsrniist'be' employed in the zfioldingopei'a'tioni' The'prop'llant compositions, having high plastic'yield points should be worked or; kneaded dining tlie moIdIiigIopei aticJn soas' to'insure unirbnirana siihstantially eempi efiuing r-tneea'se;

Extiisioiim'etliofc'lsprovi'de e kfieading pe atibn and d'ea'eii'tioii' can' b sirriultan'ebusly 'acc'ofniillished. .Thes plastic materials can beextru'ded into'cylindrical term and cufinto lengthsphoweveni it can be seen that'lintr'oduch grainsint'o a'metal casing with no' interven- Sinoe'vthe prineipal shortcomings of the=extrusion pro cedure lie in its inapplicability to high pressure operation yand ter provision-of'the necessaryt dwell period, it might ea that compres sion-molding" would; overcome, this 31?? t Y difliculty andprovide a satisfactory method forproducth piastic rnaterial uporrbein'gc'ommoldingequipmentjis' such that only the smaller propellant grains can he'molded by a single stroke of the plunger. In order to use this method on large case bonded propellants, it would be necessary to provide either tremendous magnification'of the machine, obvio'usly infeasiblefrom an economic standpoint; or to resort 7 to a multistrokeprocedure which is impractical because of still greater deaerationj problems and other obvious difficulties. v p

Bythemethbdof'the present invention, the advantages of the large volumeioperation of an extrusion procedure and'the' advantages of high pressure injection molding,

adequate working, and proper deaeration of the propellant arer'ealized without the drawbacks occasioned by'the usefof either procedure separately.

, It'is thereforean object of this invention to provide an improved method "for molding solid propellants. v

It is anotherfobject of this invention to provide a method for molding solid propellants which are free of voids.

'It"is' another object of the invention to provide a 7 method and an apparatus'formolding acase-bonded propellant which is free of voids.

Another object of the invention is to provide an improved method for high pressure molding of solid propellants.

Another object" of theinvention is to provide an improv'ed method fo'r'p'roducin'g large diameter propellant grains.

Still anotherobject of the invention is the provision of an improved method'for producing large grains of a propellant which utilizes a viscous binder.

Other and further objects and advantages of this invention'will be apparent to those skilled in the art upon study of the accompanying disclosure and-drawings'where Figure' l is'a 'scher'natic'illustration of a specific embodim'entof this'invention,

' Figure 2 is a detailed illustrationof the mold of the embodiment of Figure 1 Figure 3 is another view of'the mold in Figure 2, and

Figure 4shows a specific wiringdiagram for operating the embodiment of Figure'l.

. Broadly speaking, this invention relates to 'a method of molding solid'pr'ope'llants' which" comprises extruding the corn'pdsition through an injection chamber and into the casing-"so' a's'to substantially fill the evacuated casing receiving the charge: Additional composition 'is then forced into-the casingand -the entire charge within the casi'ngis compacted-bypressure applied to an injection pistonmoving within'the injection chamber. U

' I have discovered that the above method for molding solid propellants is particularly adapted to solid propellant compositions containinga polymeric binder and ranging inconsistency from thatrequiring about300 p.'sLi.g. to

that requiring up to about 15,000 p.s.i.g. to extrude the material through a inch orifice. The improved method of this invention makes possible the molding of large grains of solid propellant having a desired compact form, being free of voids and being free from any tendency on the part of the solid propellant to shrink from the casing upon release of the molding pressure. The major portion of the composition is introduced into the evacuated casing at a fairly high rate of flow and at a fairly low power requirement, and the final compacting step which requires expending a greater amount of power is confined to injecting a relatively minor amount of the composition into the casing. Thus the expending of a greater amount of power is restricted to a relatively minor portion of the cycle and makes possible the use of light weight equipment for the major portion of the operation of manufacturing a large propellant grain. Furthermore, the compacting pressure is maintained upon the compacted charge for a dwell period so that the strains within the semi-solid propellant are relaxed. Thus the elastic nature of the propellant is spent and there is slight tendency for the propellant to flow out of the casing When the pressure is released.

Referring now to the drawing, and particularly to Figure l, the various constituents of the propellant, as hereinbefore described, are introduced into extruder 11 through hopper 12. The material in extruder 11 is evacuated through line 13 and vacuum pump 14 at a point downstream from compacting section 15 of extruder 11. The composition passes from extruder 11 through cylinder 16, orifice 17 and into casing 18 positioned in mold 19. Extruder 11 is positioned with respect to chamber 16 so that an abrupt change of direction of propellant is avoided. When casing 18 is substantially filled with propellant composition, the back pressure exerted upon extruder 11 acts upon torque converter 21 positioned in the extruder drive shaft assembly so as to actuate switching means 22 stopping motor 23, moving valve 24 so as to cause fluid in line 25 to flow through line 25a and to act upon piston 26 for a predetermined length of time sufiicient to completely fill casing 18 with propellant composition. to compact the propellant composition and to maintain pressure upon the compacted propellant grain for a time suflicient to allow the strains within the propellant grain to become substantially equalized. At the end of the predetermined time delay, the time delay mechanism 29 closes valve 31 and operates valve 32 so as to direct the flow of fluid from line 33 through line 33b so as to act upon piston 34 in cylinder 35 and to remove mold 19 from contact with plate 36. As piston 34 moves in cylinder 35, projections 37 meet plate 38 and eject casing 18 from mold 19. When mold 19 is removed from contact with plate 36, piston 28 is permitted to travel forward in cylinder 16 until contact 39 positioned on shaft 41 connecting pistons 26 and 28 .opens switch 42. Any material remaining in cylinder 1.6

is forced out through orifice 17 and will adhere to the propellant charge in casing 18, thus leaving cylinder 16 and orifice 17 substantially free of propellant composition. When contacts 39 and 42 meet, switching means 22 operates valve 24 so as to reverse the flow of fluid from line 25 and causes piston 26 to move back through cylinder 27 to its retracted position. A cycle is started manually by operation of reset 43.

Reset 43 operates valve 32 so as to cause fluid in line 33 to flow through line 33a moving piston 34 so as to press mold 19 against plate 36. Reset 43 simultaneously opens valve 31 and resets the time delay mechanism. At the end of the cycle the operator places an empty casing in mold 19 and does any cleaning of propellant from the surface of plate 36, before starting the necessary cycle.

When mold 19 is pressed against plate 36, vacuum pump 14 begins to evacuate the casing. When pressure gauge 4 44 indicates that the mold is substantially evacuated the operator starts motor 23 by operation of reset 45.

Referring now to Figure 4; a source of electric energy is indicated at 51 controlled'by master switch 52. The cycle is started by operation of the manual reset 43 of Figure 1 which closes switch 53 shown connected to a power source 51a which can conventionally be the same as power source 51. Closing switch 53 causes current to flow through solenoid 54 so as to operate valve 32 against the tension of spring 55. Simultaneously with the flow of current through solenoid 54, current will flow through solenoid 56 opening valve 31 against the tension of spring 57.

Operation of manual reset 45 closes switch 58, starting motor 23. Torque converter 21, which can be a conventional strain gauge operated torque indicating device, transmits a potential to the grid of the tube in the thyratron circuit 59 through slip rings 64 and 65. When the back pressure on extruder 11 reaches a predetermined level, indicating that casing 18 in mold 19 is substantially filled, torque converter 21 actuates the thyratron circuit so as to cause solenoid 61 to open switch 58, which is held in open position by latch 66, stopping motor 23. The thyratron circuit simultaneously closes normally open switch 67 against the tension of spring 68 energizing solenoid 69 so as to operate valve 24 against the tension of spring 71 and to simultaneously energize time delay relay 29. After a predetermined delay interval, time delay relay 29 opens switch 53 allowing spring 55 to operate valve 32 and allowing spring 57 to operate valve 31. The removal of mold 19 from plate 36 allows piston 28 to continue its travel through cylinder 16, as shown in Figure 1, until contact 39 meets with and opens switch 42. Opening switch 42 deenergizes the thyratron circuit so as to allow spring 68 to open switch 67 so as to allow spring 71 to operate valve 24. Thus a cycle is completed.

Torque converter 21 can be any of the various torque indicating devices capable of transmitting a signal at a predetermined level of torque. The torque converter illustrated in Figures 1 and 4 is a conventional strain gauge torque indicating device wherein a strain gauge comprises one arm of a bridge circuit so that torque unbalances the bridge circuit and allows current to flow through the thyratron circuit.

The thyratron circuit is a conventional circuit and no heater connections have been shown for the thyratron tube and batterie: are shown for simplicity for tracing the circuit and describing its operation. It will be understood that any of the usual methods of energizing the circuit such as transformers and rectifiers can be used. Battery 63 energizes the grid of the thyratron tube when the bridge circuit in torque converter 21 becomes unbalanced as a result of applied torque. Battery 62 energizes the plate of the thyratron tube so that current continues to flow through the circuit after motor 23 is stopped and energy is no longer available to the grid of the thyratron tube from battery 63.

Latching switch 58 is conventional. Switch 58 is latched in open position and is released by manual reset 45. Switch 53 is manually closed by operation of reset 45 and is opened by time delay relay 29. Spring loaded solenoid valves illustrated are conventional.

Mold 19 is shown held against plate 36 by the pressure of fluid upon piston 34 in cylinder 35. However, latching means such as hydraulic clamps can be employed so as to positively lock mold 19 against plate 36 if desired. Such clamping means are well known to those skilled in the art.

As illustrated in Figure 1, hydraulic fluid is continuously pumped to hydraulic cylinders 27 and 35. How ever, if desired, the pump can be started and stopped as needed.

Better understanding of this invention will be obtained by reference to the following example, which presente'dtfon the purpose ot exniplifiiia'tion of th Eimm'p'l" A: mixture o'r is parts ofammonium nitra e; 2191 parts of a 90/ 10 ratio of butadicne/2 rnethyl-5-vinylpyridine, Mooney. c'opolymer-f (plastic: when uncured); 4.38 parts of a furnace black; 1.5l parts of :benzotr chloride; 0. 36 part of- Butyl-Eight; (dithiocarbamaten. 0.31 part of sulfur; and 0.91 part of zinc oxide is mixed so as to obtain uniform distribution of the constituents and supplying extruder 11 at a rate of 1200 pounds per hour. Extruder 11 is 11 inches in internal diameter and 1s operated at approximately 20 rpm. The propellant mixture is charged to evacuated casing 18 in mold 19 having a capacity of 80 pounds of propellant mixture. is held against plate 36 by fluid pressure upon p1ston 34 in cylinder 35. When a pressure of about 1500 p.s.1.g.

Mold 19 a is exerted upon the extruder as a result of mold 19 being determined by time delay relay 29. At the end of this dwell period of about 45 seconds, time delay relay 29 operates valve 32 so as to reverse the flow of fluid to cylinder 35 thus withdrawing mold 19 containing filled casing 18, from plate 36, and simultaneously closes valve 31. Piston 28 travels through cylinder 16 ejecting propellant through orifice 17 as mold 19 is withdrawn from plate 36 until contact 39 opens switch 42 so as to deenergize the thyratron circuit and allow spring 68 to open switch 67 deenergizing solenoid 69 so as to allow sprrng 71 to operate valve 24 reversing the flow of fluid to cylinder 27 thus returning pistons 26 and 28 to retracted position. As mold 19 is withdrawn from plate 36, projections 37 contact plate 38 and eject casing 18, filled with propellant charge, from mold 19.

A new cycle is started by placing an empty casing in mold 19, operating manual reset 43 and then operating manual reset 45 when pressure gauge 44 indicates that i the casing in mold 19 is substantially evacuated.

Variations and modifications are possible within the scope of the disclosure of the present invention, the essence of which is the provision of a novel method and apparatus for forming solid propellant charges of maximum density which comprises extruding the propellant composition into the mold through an injection cylinder and then forc ng additional propellant composition into the mold by means of a compression piston acting upon the material within the injection cylinder.

That which is claimed is:

1. The process of molding case-bonded propellants comprising a mixture having a high yield point of a solid oxidant and an uncured rubber binder which comprises introducing said mixture of solid oxidant and plastic binder into a molding zone through an intermediate zone with a minimum of change of direction of flow so as to substantially fill said molding zone; forcefully decreasing the volume of said intermediate zone at a pressure suflicient to compact said mixture in said molding zone; maintaining the pressure on said mixture for a period of time sufficient to spend the elastic nature of said mixture; and removing free gaseous material from said molding zone during the filling steps.

2. The process of molding case-bonded propellants comprising a mixture having a high yield point of a solid oxidant and an uncured rubber binder which comprises extruding said mixture of solid oxidant and rubbrybii'iderf froiii atfr' through an" intermediate" zon'e'with a" minimum chaiige' of direction of flow soas to substantially fill'said mold ing zone andsaid intermediate zone; deaeratingsaid extruding zone;said'intrmediatezone and said molding zone; subjecting said material in said intermediate zone to anadditional'pressure'sufficient to'compact said mixture in said moldirig'zone; and maintaining the pressure on-saidcomposition"in"said'molding zone for a period of time sufficient to'spen'd theielastic'n'a'ture of said propellant.

3. A device for molding semi-solid propellant material having a high yield point which comprises a mold adapted to receive a casing for containing said propellant material; extruder means; a chamber in communication with said extruder means and with said mold said extruder means and said chamber being positioned with respect to said mold so that' a minimumchange of direction of flow of said propellant material is. required; a piston adapted to move within said chamber; means for actuating said piston; means for actuating said extruder; means adapted so as to stop said extruder actuating means, to

start said piston actuating means when a predetermined back pressure is exerted upon said extruder means resulting from said mold and said chamber being substantially filled with propellant material, and time delay means to operate said piston actuating means for a predetermined time suflicient to relax strains set up in said propellant; means adapted to remove said mold from communication with said chamber after a predetermined time; and means to deaerate said extruder, chamber and mold.

4. A device for molding sem1-solid propellant material having a high yield point into a case-bonded grain which comprises a mold adapted to receive a case for containing said case-bonded grain; means for deaerating said mold; extruder means; means for actuating said extruder; cylinder means in communication with said extruder; means for placing said mold in communication with said cylinder; means for removing said mold from communication with said cylinder; a piston adapted so as to reciprocate within said cylinder;.a timedelay relay means; means for actuating said piston; torque sensitive means adapted so as to stop said extruder actuating means, to start said piston actuating means and to start said time delay relay means; and means actuated by said time delay relay means and adapted so as to remove said mold from communication with said cylinder and to eject said propellant from said mold after a predetermined time suflicient to relax strains set up in said propellant.

5. The process of molding case-bonded propellants comprising a mixture having a high yield point of a solid oxidant and an uncured rubber binder which comprises introducing said mixture of solid oxident and plastic binder into a molding zone through an intermediate zone witha minimum of change of direction of flow so as to substantially fill said molding zone; forcefully decreasing the volume of said intermediate zone at a pressure suffcient to compact said mixture in said molding zone; maintaining the pressure on said mixture for about 45 seconds to relieve strains in said mixture; and removing free ing zone and said intermediate zone; deaerating said extruding zone, said intermediate zone, and said molding zone; subjecting said material in said intermediate zone to an additional pressure sufiicient to compact said mixture in said molding zone; and maintaining the pressure riidingizone' into a molding rte 7 8 on said composition in'said molding zone for about 45 2,671,247 Lester Mar. 9, 1954 seconds to relieve the strains in said propellant. 2,675,583 Scherry, Apr. 20, 1954 7 References Cited in the file of this patent V FOREIGN PATENTS 5 655,585 Great Britain 1 July 25, 1951 UNITED STATES PATENTS 1,064,777 France 1 -De. 30, 1953 2,359,840 Goessling Oct. 10, 1944 0 1 2,469,342 Richardson May 3, 1949 OTHER REFERENCES 2,505,540 Goldhard Apr. 25, 1950 Report entitled Jet Propulsion, prepared by GALCIT 2,627,087 Hendry Feb. 3, 1953 10 for the Air Technical Service Command (1946), page 271. 

